iOS (Jailbroken): One of the key missing features on the default Apple Music app is song queuing. If you want to pick the next song that plays, you have to wait for the current song to end. Cyueue is a tweak that adds a simple "play next" button to music player.
Cyueue works a lot like the new "Up Next" feature in iTunes 11 that allows you to create playlists on the fly. When you press a song in the music player when music is playing in the background, you get the option to play now, play next or play last. When you make your choice, it's added to its own playlist and doesn't stop the currently playing track.
It's handy enough on it's own, but if you're the type to let your iPhone provide the music at a party, it makes it easy for people to add in their favourite tracks without interrupting the music.